1. Field of the Invention
The present invention relates to a drum-type washing machine, and more particularly, to a drum-type washing machine employing an induction motor for rotating the drum, in which the drum's rotational speed is accurately and stably controllable for both washing and dewatering.
2. Discussion of the Related Art
Generally, a drum-type washing machine performs washing using a frictional force between laundry and a drum, which is rotated by a transferred driving force of a motor with detergent, water, and the laundry placed in the drum. Such a drum-type washing machine prevents the laundry from being damaged and entangled and brings about such washing effects as beating and rubbing.
Referring to FIG. 1, illustrating a drum-type washing machine according to a related art, a cylindrical tub 2 made of a stainless steel based material is installed within a cabinet 1, and a cylindrical drum 3 is rotatably installed within the tub 2. A motor 5 is installed at one side under the tub 2, and a motor pulley 151 is connected to the motor 15 by a shaft. A drum shaft 31 is installed at a rear side of the drum 3, and a drum pulley 32 is installed at a rear end of the drum shaft 31. The drum pulley 32 is rotatably coupled with the motor pulley 151, which is rotatably connected to the motor 15 via a belt 16 as a power transfer element. A suspension spring 24 is installed between the inner surface of the upper part of the cabinet 1 and the outer surface of an upper part of the tub 2, to support the tub 2; and a friction damper 25 is installed between the inner surface of the lower part of the cabinet 1 and the outer surface of a lower part of the tub 2, to attenuate vibrations that develop in the tub 2 on dewatering. The tub 2 consists of a tub cover 21 forming the front of the tub 2, a tub body 22 forming the sidewall of the tub 2, and a back cover 23 forming the rear of the tub 2. A bearing housing 4, in which bearings 4a and 4b are installed, is assembled at the rear of the drum 3, to be fixed to a central portion of the back cover 23 and receive the drum shaft 31. Three wing portions 41 are integrally formed to radiate from the 120° points about the circumference of the bearing housing 4. End portions of the wing portions 41 are fixed to a rear end of the tub body 22 by a fixing bracket 14 and a bolt 8, which are assembled to be fixed to the back cover 23. Since the back cover 23 made of stainless steel and the motor 15 are installed at the rear side of the tub 2 and thus generate a weight unbalance of the tub 2, a balance weight 26 is provided to a front side of the tub 2 for compensation.
The above-constructed drum-type washing machine is driven by the motor 15, which is typically a brushless DC (BLDC) motor, a universal motor, or the like. These motors are advantageous in that their rotational speed and direction can be accurately controlled but are expensive to manufacture, and their use results in increased power consumption as well as higher production costs. In light of these problems, an induction motor has been suggested.
Nevertheless, while an induction motor may be employed to overcome such problems, it is difficult to control the rotational speed of an induction motor, which directly corresponds to the rotational speed and direction of the drum during washer operations such as washing and dewatering. Accordingly, there is a need for an apparatus enabling an accurate and stable control of the rotation of a lost-cost, low-power drum motor such as an induction motor.